|Publication number||US7791379 B1|
|Application number||US 12/547,937|
|Publication date||Sep 7, 2010|
|Filing date||Aug 26, 2009|
|Priority date||Jun 19, 2006|
|Also published as||US7598777|
|Publication number||12547937, 547937, US 7791379 B1, US 7791379B1, US-B1-7791379, US7791379 B1, US7791379B1|
|Original Assignee||Marvell Israel (M.I.S.L.) Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (11), Non-Patent Citations (2), Referenced by (1), Classifications (5), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a divisional of U.S. patent application Ser. No. 11/726,171, filed Mar. 20, 2007, which claims the benefit of U.S. Provisional Application No. 60/814,784, filed Jun. 19, 2006, and U.S. Provisional Application No. 60/815,331, filed Jun. 21, 2006, each of which is hereby incorporated by reference herein in its entirety.
This invention relates to the field of CMOS integrated circuits and, more particularly, to CMOS comparators.
A comparator is a device which is generally used to compare two voltage inputs and switch its output to indicate which of the inputs is larger. Typically comparators include at least two analog voltage inputs, which are compared to each other to determine the appropriate digital output. If the difference between the input voltages is positive then a comparator outputs a high value, and if the difference is negative then a comparator outputs a low value. Because of this behavior, comparators are popular for triggering events in digital logic based on the relative values of analog signals. For example, comparators may be used to initiate or terminate an operation depending on the difference between two particular signals.
Comparators have several performance parameters which determine their usefulness for various functions. Comparator gain is the minimum difference between the two input voltages which is required for the comparator to switch its output. A higher comparator gain corresponds to a more precise comparator. Common-mode voltage range is the range of input voltages over which a comparator functions correctly. Common-mode voltage refers to the average voltage of the input signals. A wider common-mode voltage range indicates a comparator which may interface with a wider range of input voltages. Speed corresponds to how fast a comparator's outputs respond to input-voltage changes. A higher speed indicates a quicker response time. Robustness determines how sensitive a comparator is to environmental (e.g., processing, temperature, supply voltage) variations. A more robust comparator corresponds to a less sensitive comparator. Range of output swing determines the difference between the high output value and the low output value. A larger output swing indicates a greater difference between the voltage levels of high and low outputs.
A comparator with a high output swing is traditionally preferable because it easily interfaces with logic circuits requiring large input swings. For example, the term “rail-to-rail output swing” is commonly used to denote an output swing which goes from ground to the supply voltage. These large output swings may be important to ensure the proper functioning of the subsequent digital logic.
Typically, comparator design seeks to maximize each of these different parameters to create a comparator with all around solid performance. However, in some instances it may be desirable to sacrifice certain parameters for higher performance in others. For example, in some comparator applications a higher speed may be valued over a larger output swing.
It would therefore be desirable to design a comparator with a high-speed reduced-output-swing. It would also be desirable for this high-speed reduced-output swing comparator to have a self-biased configuration, a fully-complementary design, and a rail-to-rail input common-mode range.
In accordance with the invention, a CMOS comparator having a high-speed reduced-output-swing is provided. The high-speed reduced-output-swing comparator may have a fully complementary CMOS design, be self-biased, and have a rail-to-rail input common-mode range. The self-biasing scheme yields a robust comparator with a low sensitivity to temperature, processing variations, supply-voltage variations, and common-mode input voltages. The fully-complementary design leads to a physically small device with low power consumption. The rail-to-rail input common-mode range leads to a versatile comparator which may take a wide range of inputs. The high-speed reduced-output-swing allows for a quick output response to changes in the input.
Further features of the invention, its nature and various advantages, will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.
The objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:
Input signals 104 and 105 may be broken down into individual voltage sources 101, 102, and 103 in order to define the operating conditions of comparator 110. Common voltage source (VCOM) 101 represents the voltage level which is present in, or common to, both inputs 104 and 105. VCOM 101 may be generally defined as the average of two input voltages INP 104 and INN 105. Two other voltage sources 102 and 103 offset INP 104 and INN 105 from VCOM 101. Given that VCOM 101 is the average of the two input voltages, INP 104 is VCOM 101 offset by some magnitude in the positive direction and INN 105 is VCOM 101 offset by the same magnitude in the negative direction. This relationship may be represented as
In the above equations VDIFF is the difference between the two input nodes INP 104 and INN 105 which may be expressed as
V DIFF =V INP −V INN. Equation 3
If VDIFF is positive, comparator output 120 will read a logic high. If VDIFF is negative, comparator output 120 will read a logic low.
Given that the comparator in
For most applications, a comparator with a high comparator gain, a large common-mode voltage range, high-speed outputs, robust operating capability, and large output swings is desirable. Special circumstances arise where some parameters are a higher priority than others. For example, a higher comparator gain could be more valuable than a large common-mode voltage range in a small signal analog-to-digital converter application where the designer expects a limited range of inputs.
In accordance with the present invention, a larger output swing may be sacrificed in the interest of increased speed.
Ideal comparator output 230 could be expected from a theoretical device such as ideal comparator 110. Output 230 shows rail-to-rail output swings as well as instantaneous response times. However, non-ideal comparators are not capable of producing output 230 due to physical limitations, such as transistor switching times.
Typical comparator output 240 provides a rail-to-rail output swing which could be useful when interfacing with digital circuits which require large input swings. One drawback to output 240 is that this signal takes longer to reach the common-mode voltage level when switching states.
High-speed Reduced-output-swing Comparator output 250 exhibits increased switching speed due to reduced output swing when compared to typical output 240. This feature may be seen by analyzing comparator outputs in response to input change events. In response to a change in the inputs, the outputs of the HRC comparator may initially have a higher rate of change than the outputs of a typical comparator. After crossing the common-mode voltage level, the rate of change of the HRC outputs can slow down to less than the slope of typical comparator outputs. In many cases, the most important measurement of the outputs' speed can be the time required for the outputs of the comparator to cross the common-mode voltage level, and the time required for the outputs to reach the final output state might be less important. In this situation, a slower rate of change after crossing the common-mode voltage level might not have a significant impact on the relevant speed measurements.
For example, INP exceeds INN at event 291. Shortly thereafter, HRC output 250 crosses its common-mode voltage level at time 251. Some time later, typical output 240 crosses its common-mode voltage level at time 241. This difference in speed is also present when the outputs transition from a high to a low state, for example in response to event 292. It is contemplated that a complementary differential output could be provided in combination with HRC output 250.
Transistors 320 a, 321 a, 324 a, 325 a, 320 b, 321 b, 324 b and 325 b may be p-type metal-oxide semiconductor field-effect transistors (MOSFETs). Transistor 322 a, 323 a, 326 a, 327 a, 322 b, 323 b, 326 b and 327 b may be n-type metal-oxide semiconductor field-effect transistors (MOSFETs).
It is to be noted that comparator 300 is symmetrical and all of the transistors are comprised of matched device pairs. The matched pairs are denoted by having the same reference numeral and are differentiated by the suffix a or b. For example, transistors 321 a and 321 b comprise one of the matched pairs.
It is to be further noted that comparator 300 is completely complementary since each transistor device has a complementary counterpart of the opposite conduction type. Transistor 320 a is complementary to transistor 323 a; transistor 321 a is complementary to transistor 322 a; transistor 324 a is complementary to transistor 327 a; and transistor 325 a is complementary to transistor 326 a. Note that these complementary relationships are also true for each transistor's matched pair.
There are several beneficial characteristics of comparator 300. For example, the design of comparator 300 internally incorporates negative feedback into each output. Therefore, unlike some comparator circuits, an external biasing circuit is unnecessary. Negative feedback may be provided for OUTP 305 by coupling output node 310 with the gates of transistors 320 b, 323 b, 324 b, 325 b, 326 b, and 327 b. Therefore any unwanted changes in the voltage of OUTP 305 may be compensated primarily by a change in the behavior of transistors 324 b, 325 b, 326 b, and 327 b and the behavior of transistors 320 b and 323 b, to a lesser extent.
This negative feedback, self-biasing scheme compensates for variations in operating conditions, fabrication, or common mode input voltage. The self-biasing scheme also contributes to the attenuation of common-mode input components. This attenuation allows HRC 300 to operate over a wide range of common-mode input voltages.
In accordance with one embodiment of the present invention, a complementary output, for example OUTN 306, may be included in the circuit. The negative feedback configuration described above may be applied to the complementary output node 311 as well.
Another advantage of comparator 300 is the reduced output swing. Output swing, also called output range, may be defined as the voltage difference between a high and low output. One way to set the output swing magnitude of comparator 300 is to change the size of devices 324A-327A with respect to devices 320A-323A, as well as the size of devices 324B-327B with respect to devices 320B-323B. For example, if the size of transistors 324A-327A and 324B-327B are decreased with respect to the size of transistors 320A-323A and 320B-323B the output swing can be increased.
In the system shown in
Even though the output switching level described above (i.e., 0.2V) is less than rail-to-rail, it is sufficient for controlling a current switch. Therefore, by sacrificing the range of the output swing, a much faster comparator can be used in accordance with an embodiment of the present invention. While the embodiment shown in
Referring now to
Referring now to
The HDD 1000 may communicate with a host device (not shown) such as a computer, mobile computing devices such as personal digital assistants, cellular phones, media or MP3 players and the like, and/or other devices via one or more wired or wireless communication links 1008. The HDD 1000 may be connected to memory 1009 such as random access memory (RAM), low latency nonvolatile memory such as flash memory, read only memory (ROM) and/or other suitable electronic data storage.
Referring now to
The DVD drive 1010 may communicate with an output device (not shown) such as a computer, television or other device via one or more wired or wireless communication links 1017. The DVD 1010 may communicate with mass data storage 1018 that stores data in a nonvolatile manner. The mass data storage 1018 may include a hard disk drive (HDD). The HDD may have the configuration shown in
Referring now to
The HDTV 1020 may communicate with mass data storage 1027 that stores data in a nonvolatile manner such as optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in
Referring now to
The present invention may also be implemented in other control systems 1040 of the vehicle 1030. The control system 1040 may likewise receive signals from input sensors 1042 and/or output control signals to one or more output devices 1044. In some implementations, the control system 1040 may be part of an anti-lock braking system (ABS), a navigation system, a telematics system, a vehicle telematics system, a lane departure system, an adaptive cruise control system, a vehicle entertainment system such as a stereo, DVD, compact disc and the like. Still other implementations are contemplated.
The powertrain control system 1032 may communicate with mass data storage 1046 that stores data in a nonvolatile manner. The mass data storage 1046 may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in
Referring now to
The cellular phone 1050 may communicate with mass data storage 1064 that stores data in a nonvolatile manner such as optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in
Referring now to
The set top box 1080 may communicate with mass data storage 1090 that stores data in a nonvolatile manner. The mass data storage 1090 may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in
Referring now to
The media player 1100 may communicate with mass data storage 1110 that stores data such as compressed audio and/or video content in a nonvolatile manner. In some implementations, the compressed audio files include files that are compliant with MP3 format or other suitable compressed audio and/or video formats. The mass data storage may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. At least one HDD may have the configuration shown in
Thus it is seen that circuitry for a high-speed reduced-output-swing self-biased fully-complementary CMOS comparator with rail-to-rail input common-mode range is provided. One skilled in the art will appreciate that the invention may be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation, and the present invention is limited only by the claims which follow.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US9209790||Dec 19, 2014||Dec 8, 2015||Freescale Semiconductor, Inc.||Low voltage, self-biased, high-speed comparator|
|U.S. Classification||327/63, 327/50|